Control device



June 1956 R. D. DONALDSON 2,751,457

CONTROL DEVICE Filed Feb. 25, 1954 42 4| 1 35 3 \J I x 7 T34... I 40 35 2- i4 2| 1 I \37 A l8 3 l5 u E l4 INVENTOR.

ROBERT D. DONALDSON 15. Z BY United States Patent CONTROL DEVICE Robert D. Donaldson, Anoka, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application February 25, 1954, Serial No. 412,482

9 Claims. (Cl. ZOO-81.5)

This invention relates to pressure switches and more particularly to differential pressure switches with a double metal seal between switch contacts and conditions being sensed.

One embodiment of my invention has two bellows mounted on a base plate within a sealed casing. Pressure connections in the base plate communicate with the interiors of the bellows. A lever interconnects the movable ends of the bellows and the lever has extensions ending in knife edges forming the pivotal axis of the lever. The top plate of the sealed casing has a flexible diaphragm forming the center portion thereof. The lever has an extension protruding through the diaphragm and the pivotal axis of the lever is in the plane of the diaphragm and passes through the center thereof. A second lever is attached to the extension and operates switch contacts. A spring means is attached to one end of the second lever and applies a force to bias the levers in one direction so as to cause the knife edges to engage the top plate.

My invention allows the transmission of motion from the sensing means to the switch contacts with a doublenietal seal between the fluid and the switch contacts.

One of the places my invention could be utilized would be in a switch controlling a heater for a fuel filter in aircraft. If the fuel filter starts to ice up the differential between the upstream and downstream fuel pressure increases. This increase in differential would operate the switch turning on the heater to de-ice the fuel filter. A drop in the differential due to completion of the de-icing of the fuel filter will open the switch turning off the heater. For safety purposes it is required in aircraft to use a double metal seal between an inflammable liquid and switch contacts.

My invention can be used in many other places for transmission of mechanical movement through a metal seal as required.

Therefore, an object of my invention is to provide a control device of the type described that is simple in construction, light in weight and reliable in operation.

Another object of my invention is to provide a control device of the type described that has a double metal seal between an inflammable liquid and switch contacts for sensing the pressure of the inflammable liquid.

Other objects and advantages of my invention will in part be obvious and in part be described when the following specification is read in conjunction with the drawing in which Figure 1 is a cross-section of an embodiment of my invention and Figure 2 is a perspective view of the same embodiment of my invention with most of the casing cut away.

Referring now to the drawing, a sealed casing 10 has a base plate 11 with pressure connections 14 and 15. Two bellows 18 and 19 are attached to the base plate 11 within casing 10 and pressure connections 14 and 15. A lever 21 interconnects the free ends of bellows 18 and 19. As best shown in Figure 2 lever 21 has two oppositely disposed extensions 28 and 29 terminating in knife edges 31 and 32'. A top plate 34 of casing 111 has 2 a flat inner surface with a circular opening therein which is closed by a generally flat diaphragm 35 of larger diameter than the opening in top plate 34. The diaphragm 35 is sealed to the casing unit annular area. The diaphragm 35 is shown as flat though it is not intended to restrict my invention to an entirely flat diaphragm as it is evident to any experienced in the art a diaphragm with corrugations or convolutions could be used and in some cases may be desirable. For example, a diaphragm of the type disclosed in application Wilbur A. Martin, Serial No.- 198,6-72, filed December 1, 1950, now Patent 2,677,741 may be used. Top plate 34 has V slots 36 and 37 that are engaged by knife edges 31 and 32. Lever 21 has abutments 38 and 39 which act as mechanical stops and limit the motion of lever 21 and expansion of bellows 18 and 19. The casing 10 may be filled with an inert gas. An

extension 40 of lever 21 protrudes through diaphragm 35* and is sealed thereto. A lever 41 is fastened to extension 40 by screw 42. A spring 46 is attached to lever 41 and a hole 47 in lever 41. The spring 46 applies a force to lever 41 which biases levers 41 and 21 in a clockwise direction and biases knife edges 31 and 32 in V slots 36 and 37 against top plate 34 so that the pivotal axis of levers 41 and 21 lies in the plane of diaphragm 35 and passes through the center of diaphragm 35. Theoretical ly, the pivotal axis of levers 41 and 21 should be in the center plane of the diaphragm 35. However, a thin diaphragm is used and then the pivotal axis is at the top side of the diaphragm 35, which is sufliciently close to the ideal condition for practical purposes. A thin diaphragm is used to keep the internal stresses low and to avoid adding unduly to the spring rate of the device. Lever 41- has an extension 49 that closes switch contacts 51- and 52 on counterclockwise rotation of levers 41 and 21. This counterclockwise rotation will be caused by a higher pressure in bellows 18 and 19. Rotation is resisted by spring 46; by adjusting the tension on spring 46 by a screw 54 the control point can be adjusted.

Broadly, the invention contemplates any arrangement by which mechanical. motion is transmitted through a flexible diaphragm by means of pivotal abutments on opposite sides of the center of the diaphragm with no appreciable translation of the center of the diaphragm. It will be readily apparent that in accordance with my invention many changes may be made in details of the construction and arrangement of the parts. For example, the top plate is shown as generally flat and has the V slots to be engaged by the knife edges. It is not neces sary that the top plate be flat for a casting of different shapes could be used. Also as there is little rotation of the levers necessary to operate the switch contacts the V slots are notnecessary. It is necessary that the pivotal axis is located so that it passes through the center of the diaphragm. The disclosed construction provides a simple and effective way of. accomplishing this. The scope of my invention. is accordingly defined by the appendedclaims.

I claim as my invention:

1. In a control device comprising, a sealed casing including a base plate having two pressure connections therein and a top plate with. a circular opening. therein which is closed by a generally flat diaphragm of larger diameter than. the opening and sealed to the casing in an annular area, two bellows within said casing each attached to said base plate and each. having its interior communicating with a pressure connection, a. lever interconnecting the free ends of said bellows, said lever having two.

extending normal to the pivotal axis and through the center of said diaphragm, a second lever carried outside of said casing and said lever portion, switch contacts actuated by said second lever and spring means acting on said second lever biasing said levers in one direction about the pivotal axis, the force of said spring means being applied in a direction to bias said knife edges against the top plate of said casing.

2. A control device comprising, a sealed casing including a base plate and a top plate with a flexible metal diaphragm forming the center portion of said top plate of said casing, two bellows within said casing, each of said bellows attached to said base plate each at a pressure connection in said base plate, said pressure connections each opening into one of said bellows, a lever interconnected to the movable end of each of said bellows, first and second oppositely disposed lateral extensions extending from the center of said lever, said first and second extensions each terminating in pivotal abutments engaging said top plate of said casing radially removed from said flexible center portion of said top plate, said pivotal abutments establishing a pivotal axis for said lever in the plane of said diaphragm passing through its center, abutments on said member opposite the interconnection to the movable end of said bellows, said abutments limiting the amount of rotation of said member upon abutting on said top plate, a third extension of said lever at the center of said lever normal to the pivotal axis and through said diaphragm, said extension attached and pressure sealed to said diaphragm, a second lever attached to said third extension outside said casing, said second lever responding through said first lever and said third extension to the differential pressure between said two bellows, and a switch means actuated by said second lever.

3. A control device comprising, a differential sensing means, a frame supporting said differential sensing means, a solid member carried by said frame, said solid mem ber actuated by said differential sensing means, said member being operatively attached to said sensing means, a pair of pivotal abutments on the opposite side of said member from the points of operative attachment of said member to said sensing means, said two pivotal abutments positioned so a line connecting said two pivotal abutments would intersect a line connecting the points of operative attachment of said member to said sensing means, an extension of said member at said intersection of two lines, a plane surface forming the top of said frame, a flexible diaphragm forming a center portion of said surface, said plane surface engaged on the bottom side by said two pivotal abutments, said extension of said member protruding through and rigidly attached to said diaphragm, a lever attached to said extension on the opposite side of said diaphragm from said member, a control means actuated by said lever in response to said differential sensing means.

4. A control device comprising, a displacement sensing means, a solid member actuated by said displacement sensing means, two pivotal abutments on said member, a plane surface, a diaphragm forming the center portion of said plane surface, said two pivotal abutments engaging said plane surface on opposite sides of the center of said diaphragm, an extension of said member protruding through and attached to said diaphragm, a control means actuated by said extension of said member.

5. A control device comprising, a displacement sensing means, a solid member actuated by said displacement sensing means, two pivotal abutments on opposite ends of said member, a plane surface, a diaphragm forming the center portion of said plane surface, an extension of said member protruding through and rigidly attached to said diaphragm, said plane surface engaged by said pivotal abutments on said member such that the pivotal axis of said member is in the plane of said diaphragm, a switch means actuated by said extension of said member.

6. A control device comprising, a displacement sensing means, a solid member actuated by said displacement sensing means, two pivotal abutments on said member, a top plate, a diaphragm so mounted in said top plate that the plane of the periphery of said diaphragm and the center of said diaphragm are in the same plane, said pivotal abutments engaging said top plate radially re moved from diaphragm and establishing a pivotal axis for said member in the plane of the periphery and center of said diaphragm and passing through the center of said diaphragm, an extension of said member protruding through and attached to said diaphragm, a control means actuated by said extension of said member.

7. A control device comprising, a frame including a flat top plate and a flat diaphragm forming the center portion therein, a pressure responsive sensing means mounted on said frame, a lever actuated by said pressure responsive sensing means, said lever having two oppositely disposed lateral extensions terminating in pivotal abutments engaging said top plate of said frame radially removed from said diaphragm center portion of said top plate, said pivotal abutments establishing a pivotal axis for said lever in the plane of said diaphragm and passing through its center, an extension of said lever protruding through and rigidly attached to said diaphragm, a second lever attached to the end of said extension of said first lever, switch contacts actuated by said second lever and spring means acting on said second lever biasing said levers in one direction about the pivotal axis, the force of said springs means being applied in a direction to bias said pivotal abutments against the top plate of said frame.

8. A control device comprising, a sealed casing with a base plate thereto, a pressure responsive means within said casing attached to said base plate, a solid member, said solid member operatively connected to said pressure responsive means and actuated thereby, two pivotal abutments on opposite ends of said member, a generally plane surface forming the top of said casing, a diaphragm form ing the center portion of said plane surface, the inner side of said plane surface engaged by said pivotal abutments in said member radially removed from said diaphragm portion of said plane surface such that the pivotal axis of said member is in the plane of said diaphragm and passes through the center thereof, an extension of said member protruding through and rigidly attached to said diaphragm, a lever attached to the end of said extension, switch contacts actuated by said lever.

9. A control device comprising, a sealed casing with a base plate thereto, two bellows within said casing attached to said base plate, a means for connecting said bellows to a pressure differential, a solid member operatively connected to the movable end of said two bellows, pivotal abutments at opposite ends of said member, a normally plane surface forming the top of said casing, a diaphragm'having a normally plane surface forming a center portion of said plane surface, either side of said plane surface engaging the pivotal abutments of said member radially removed from said diaphragm portion of said plane surface such that the pivotal axis of said member lies in the plane of said diaphragm and passes through the center thereof, an extension of said member protruding through and rigidly attached to said diaphragm, said member normally biased to said pivotal abutments on said member engage said plane surface, a lever rigidly attached to the end of said extension of said lever, and switch contacts actuated by said lever.

References Cited in the file of this patent UNITED STATES PATENTS 2,115,431 Shively Apr. 26, 1938 2,355,951 Coffeen et al. Aug. 15, 1944 2,418,759 Crimmins Apr. 8, 1947 FOREIGN PATENTS 684,356 Germany Nov. 27, 1939 

